Virtual line switched ring (VLSR) connection state distribution scheme

ABSTRACT

Systems and methods consistent with this invention allow for each node within one or more rings to obtain connection and topology information from other nodes within these rings. In such a system, each node is able to maintain connection table and topology tables for each node and each ring within a ring network. In particular, such information can be kept current because this scheme allows for dynamic updating of connection and topology information in real time. With such current information, a node is able to utilize this information to execute such operations as squelching connections on a protect line and timeslot interchange. In addition, by supporting timeslot interchange, the ring can be managed as more than a single logical entity as well as can have better bandwidth management utilization.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/421,062, entitled “VIRTUAL LINE SWITCHED RING,”filed on Oct. 19, 1999 and related to U.S. patent application Ser. No.09/259,263, filed Mar. 1, 1999, entitled “ROUTING AND SIGNALING IN ASONET NETWORK”, both of which are incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a method and system forimplementing a virtual line-switched ring connection state distributionscheme within a line switched ring network carrying optical signals inaccordance with a synchronous optical network (SONET) standard.

[0003] SONET networks often have a ring configuration including acollection of nodes forming a closed loop. FIG. 1 illustrates an exampleof a conventional SONET bi-directional ring 100 whereby information mayflow in either a clockwise or counterclockwise in the figure, asindicated by arrows labeled “working” and “protect”. Add-dropmultiplexers (A/D mux) 110, 120, 130 and 140 add and/or drop signals toswitch data from one span (SP1 to SP7) to another. Ring 100 is thustermed a “bi-directional line switched ring” or BLSR, and datatransmitted in such a ring typically must conform to a particularprotocol.

[0004] As further shown in FIG. 1, each of spans SP1 to SP7 includes oneworking line and a corresponding protection line. For example, spans SP1and SP5 interconnect A/D muxes 110 and 120 and include working linescarrying data in opposite directions. The working lines within each ofthese spans further include respective protection lines for transmittingdata in the event the associated working line fails.

[0005] The SONET ring provides protection for transmission of data intwo way. First if a working lines fails, the corresponding protectionlines may be used. In the alternative, if working lines fail between twoA/D muxes, any communication route directed through the failed line maybe rerouted through the A/D muxes through a process known as spanswitching. For example, if the working lines between A/D mux 110 and A/Dmux 120 fail, instead of using the corresponding protection lines,communications may be sent from A/D mux 110 to A/D mux 120 via A/D mux140 and 130.

[0006] Typically, the working and protect lines are provided in a fiberoptic bundle. Accordingly, if the working line fails, due to a fibercut, for example, the corresponding protect line often will also fail.Span switching is thus often preferred to simply switching data from thefaulty working line to the protect line. Both schemes may be used inconjunction with each other, however, whereby an attempt is first madeto use the protect line when the associated working line fails, andthen, if the protection line is itself faulty, span switching is used toredirect communications.

[0007] The SONET standard has a plurality of optical levels and logicallevels that represent the amount of optical information a line iscapable of carrying at a given time. These different optical levels arereferred to as OC-n, where n is indicative of the bandwidth or capacityassociated with the line. Current SONET bi-directional rings requirethat all spans carry data at the same optical rate because A/D muxes canonly direct communications from one line to another having the same OC-nlevel. Therefore, BLSR requires that all lines in the network are of thesame type and that each span between A/D muxes has the same number oflines.

[0008] In accordance with the SONET standard, spans transfer units ofinformation called Synchronous Transport Signals (STS). For thedifferent optical carrier levels OC-n (such as OC-1, OC-3 and OC-12),there is a corresponding STS-n, where n is the number of STS-1 segmentsor time slots. Typical spans are composed of 1, 3, 12, 48, or 192STS-1's. All SONET spans transmit 8,000 frames per second, where eachframe is composed of an integer number of STS-1 segments, such as 1, 3,12, 48 or 192.

[0009] Each STS-1 segment includes a payload section and an overheadsection. The overhead includes K-bytes that communicate error conditionsbetween spans in a network and allow for link recovery after networkfailure. K-byte signaling takes place over the protection lines. In aseries of STS segments, only K-bytes from the first STS-1 segment areused to carry error data. Current SONET networks make no use of theframing overhead of the remaining STS-1 segments. The series of STS-1segments only carries K-byte error information for a single ring.

[0010]FIG. 2 illustrates an example of a connection between two rings200 and 210 using four SONET A/D multiplexors. Specifically, A/D mux 202of ring 200 is coupled to A/D mux 212 of ring 210, while A/D mux 206 ofring 200 is coupled to A/D mux 216 of ring 210. Data is transmitted onthese connections at a slower rate than through rings 200 and 210. Thus,a total of four “matched” A/D mux nodes are often required to connecttwo rings. Typically, each such pair of A/D muxes is dedicated toproviding ring-to-ring connections, and are not configured to passinformation around a ring and forward information to another ring at thesame time.

[0011] In the SONET network ring environment, there currently does notexist a system, which allows a ring node to automatically manageconnection and topology information regarding the ring as well as tomanage the ring as more than a single logical entity.

SUMMARY OF THE INVENTION

[0012] Systems and methods consistent with this invention allow for eachnode within one or more rings to obtain connection and topologyinformation from other nodes within these rings. In such a system, eachnode is able to maintain connection table and topology tables for eachnode and each ring within a ring network. In particular, suchinformation can be kept current because this scheme allows for dynamicupdating of connection and topology information in real time. With suchcurrent information, a node is able to utilize this information toexecute such operations as squelching connections on a protect line andtimeslot interchange. In addition, by supporting timeslot interchange,the ring can be managed as more than a single logical entity as well ascan have better bandwidth management utilization.

[0013] Both the foregoing general description and the following detaileddescription explain examples of the present invention and do not, bythemselves, restrict the scope of the appended claims. The accompanyingdrawings, which constitute a part of this specification, illustratesystems and methods consistent with the invention and, together with thedescription, help explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated in andconstitute part of this specification, illustrate embodiments of theinvention and, together with the description, serve to explain theadvantages of the invention. In the drawings,

[0015]FIG. 1 shows a bi-directional line switched ring according to theprior art;

[0016]FIG. 2 shows two connected bi-directional rings according to theprior art;

[0017]FIG. 3 shows a virtual line switched ring in accordance with thepresent invention;

[0018]FIG. 4A shows a switch and line card in accordance with thepresent invention;

[0019]FIG. 4B shows a connection state distribution protocol module inaccordance with the present invention;

[0020]FIG. 5 shows two connected virtual line switched rings inaccordance with the present invention;

[0021]FIG. 6 shows three connected virtual line switched rings sharing aprotection line in accordance with the present invention;

[0022]FIG. 7 shows a virtual line switched ring having varying numbersand types of lines between switches in accordance with the presentinvention;

[0023]FIG. 8 shows the steps of adding a line to a virtual line switchedring in accordance with the present invention;

[0024]FIG. 9 shows the steps for deleting a line form a virtual lineswitched ring in accordance with the present invention;

[0025]FIG. 10 shows the steps for validating a new line configuration ina virtual line switched ring in accordance with the present invention;

[0026]FIG. 11 illustrates a process for assigning working lines toprotection lines; and

[0027]FIG. 12 illustrates two SONET ring networks configured inaccordance with a feature of the present invention.

[0028]FIG. 13 illustrates a SONET ring network configured in accordancewith a feature of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The following detailed description refers to the accompanyingdrawings. The same reference numbers in different drawings identify thesame or similar elements. Also the following detailed description doesnot limit the invention. Instead, the scope of the invention is definedby the appended claims.

[0030] Systems and methods consistent with the principles of the presentinvention provide a SONET ring network that uses switches at the nodesallowing for sharing a switch to connect a plurality of rings. Thepresent invention also provides for sharing a protection line between aplurality of rings by utilizing overhead provided for in the SONETstandard. Finally, the present invention provides for having a differentnumber and-type of lines between nodes by using switches and analgorithm to regulate the updating of the lines.

[0031] The present invention, as shown in FIG. 3, uses switches as nodesin a SONET network. For example, SONET ring 300 includes switches 310,320, 330 and 340 coupled to various working and protection lines.Specifically, there are two working lines and two protection linesbetween each pair of switches. Information is transferred through SONETring 300, typically in a time division multiplexed fashion, throughpluralities of input and output ports in each switch.

[0032]FIG. 4A shows an example of a switch consistent with the presentinvention. Switch 410 includes controller 412, manager module 413, spanwest lines 414, span east lines 416, a Connection State DistributionProtocol (“CSDP”) manager 415 and a dispatcher circuit 418. Controller412 oversees general operations of the switch 410 and is used by themanger module 413 and dispatcher 418 to process and forward information.Manger module 413 manages virtual lines of span west lines 514 and spaneast lines 416. FIG. 4B illustrates a more detailed embodiment of theCSDP Manager 415. The CSDP Manager 415 includes a CSDP controller 475, aquery module 450, a configuration module 455, a state module 460, aconnections table 465 and a topology table 470. The CSDP Manager 415 isresponsible for providing the switch 410 with the ability toauto-discover the connection characteristics of each node and thetopology of the ring. The CSDP controller 475 is coupled to the querymodule 450, the configuration module 455, the state module 460, theconnections table 465 and the topology table 470. The CSDP controller475 is responsible for managing the generation and processing of CSDPmessages, which are transmitted and/or received by the switch 410. Thequery module 450 is responsible for processing and generating CSDP querymessages. The configuration module 455 is responsible for processing andgenerating CSDP config messages. The state module 460 is responsible forprocessing and generating CSDP state messages. The connections table 465includes connection information for each node on a ring. The topologytable 470 includes topology information for each ring in a network. Thedata contained within the connections table 465 and the topology table470 can be accessed by any module within the switch 410 in order toperform operations in configuring the node as well as to determiningadditional relationships as to the various nodes within the ring.Dispatcher 418 receives and processes data from external sources.

[0033] Switch 410 is connected to a line card 420 having an aggregator422 and a plurality of monitor modules 424 _(l) to 424 _(n). Aggregator422 gathers information from monitor modules 424 and passes theinformation to appropriate switches via monitor modules 424. Eachmonitor module 424 has a plurality of physical SONET lines 430 thatconnect to other switches. Physical lines 430 are logically designatedby switch 410 to correspond to virtual lines associated with the spanwest lines 414 and span east lines 416. Span west lines 414 and spaneast lines 416 define the logical mapping between physical lines andlogical lines, where the logical lines may come from any combination ofmonitor modules 424. The designation of west and east lines is only alogical designation. This logical designation is used to distinguishbetween the different network nodes to which switch 410 is connected. Inone embodiment, the span west lines 414 define logical lines leading toone switch in the network, while the span east lines 416 define logicallines leading to another switch in the network.

[0034] Since switch 410 simultaneously transfers information between aplurality of different SONET lines of information, the present inventionallows for two rings to share a switch, or be connected by sharing aswitch. For example, as seen in FIG. 5, SONET network ring 500 and SONETnetwork ring 510 are connected by sharing switch 508. Ring 500 includesswitches 502, 504, 506, and 508. Ring 510 includes switches 508, 512,514, and 516. By using a single switch to connect rings, information ispassed over SONET lines at the same rate between rings as is passedwithin a single ring.

[0035] More than two SONET rings may share a switch. As shown in FIG. 6,three SONET rings share two switches. Ring 600 includes switches 601,602, 603, and 604. Ring 610 includes switches 603, 604, and 612. Ring620 includes switches 603, 604, 622, 624, and 626. As furtherillustrated in FIG. 6, each working and protect line in ring 600 isassigned a particular identifier, e.g., working line one (w1) andprotection line 1 (p1).

[0036] In addition to sharing switches among rings, the rings of FIG. 6share protection line p4 (605). Moreover, between each switch and itsneighbor there is a working line, which is shown as a solid line, and aprotection line, which is shown as a dotted line. Three working linesconnect switch 603 to switch 604, one for each ring, and one protectionline 605 which is shared by all of the rings. The sharing of aprotection line is not required between these switches; three dedicationprotection lines could have been provided between these two switchesinstead. When rings share a protection line, however, the protectionline is allocated for use on a first-come, first served basis.Individual STS-1 segments on the protection line are allocated toreplace the working lines on an STS-1 segment basis. One protection linemay carry portions of STS-1 segments from more than one working line.

[0037] Multiple rings may share a protection line by utilizing K-bytesignaling on multiple STS-1 segments. As previously discussed, K-bytescarry error information related to line failures for a ring. Errorsnoted in the K-byte may initiate switching between a working andprotection line. For example, criteria for switching between a workingand protection lines are generally the same, and may include loss ofsignal, loss of frame, an alarm indication signal, or a single failure.In which case, K-byte codes may include: block out of protection code,forced span switch code, forced ring switch code, signal fail-span code,signal fail-ring code, and signal degrade code, among others.

[0038] Conventional BLSR only allows for one ring to use a protectionline and only uses the first K-bytes from the first STS-1 in a series ofSTS-1 segments to report errors for the single ring. Even though notused, the current SONET protocol includes K-byte overhead in each STS-1of a series of STS-1 segments for additional rings. The presentinvention uses these K-bytes in the succeeding STS-1 segments to realizeshared protection lines. In particular, each ring has separate K-byteinformation to reflect errors within the ring. When one or more ringsuse a protection line, the K-byte information is carried over thatprotection line for each ring, and is carried in respective sequentialSTS-1 segments. The switches on either end of the protection line thatis being shared are programmed with information defining which STS-1segment is carrying the K-byte information for which ring. For example,the first segment may contain the K-byte information for ring 610, andthe third segment contains the K-byte information for ring 620. Switches603 and 604 are thus programmed with information defining which STS-1segment carries the K-byte information for which ring based on thereceived order of the STS-1 segments. In addition, K-byte informationconcerning the availability of a particular protection line is passed toother switches in the rings through appropriate signaling, as discussedin greater detail below.

[0039] Returning to FIG. 4A, monitor module 424 monitors incomingK-bytes. More particularly, monitor module 424 monitors incoming K-bytesfor changes indicating an error. When a K-byte change for a particularring is maintained for at least three consecutive frames monitor module424, monitor module 424 reads the value of the K-bytes and sends thechange to aggregator 422. Aggregator 422 queues the K-byte informationfrom other monitor modules 424, and after a period of time, such as onemillisecond, sends a message to switch 410 that includes the K-bytechanges, and the lines that have signal failure or degradation.Dispatcher 418 parses the message from the aggregator 422 and sends lineinformation to span west lines 414 or span east lines 416 if either ofthese utilize the line in question. The span receiving the lineinformation may do nothing if higher priority conditions exist, or mayinitiate a line switch, ring switch, or route change.

[0040]FIG. 11 illustrates steps of a process 11 for mapping workinglines to corresponding protections lines. The mapping is performed on afirst-come, first served basis, and should conform to an orderingdictated by a network administrator. In a first step 1110, a first STS-1on a first working line is mapped to a first STS-1 of a first protectionline. In step 1120, the next STS-1 of the working line is mapped to thenext available STS-1 of a protection line. Each remaining STS-1 of theworking line is mapped to a respective STS-1 on a protection line (step1130). Steps 1110 through 11130 are repeated for each remaining workingline (step 1140).

[0041] The invention will next be described by way of example withreference to FIG. 12 showing first and second rings 1200 and 1205.Within ring 1200, working traffic originating at switch 1230 andterminating at switch 1220 is passed along span 1225 in a east-westdirection as indicated by arrow 1226. If a break occurs in span 1226 (asindicated by an “X”), traffic is rerouted through switches 1210 and 1240using a shared protection line in span 1227, which is assigned inaccordance with processes and structures identified above. In this case,a K-byte ring switch signal is supplied from switch 1230 to switch 1240and then to switches 1210 and 1220 to thereby indicate use of theprotection line in ring 1205, at least for particular time slots soaffected by the break in span 1226. Switch elements in ring 1200,however, must further follow an arbitration protocol whereby theprotection line in span 1227 is rendered not available to them, at leastfor-those time slots. Accordingly, switch 1230 passes known K-bytelockout-protection span (LP-S) data to switch 1240, which in turn,forwards this data to remaining switches 1260 and 1250 in ring 1200.Thus, information concerning availability of a particular protectionline, as well, as information concerning a fault in a particular span isdistributed amongst-the switching elements of a given network throughK-byte signaling.

[0042] In another embodiment, systems and methods consistent with theprinciples of the present invention utilize a varying number and type oflines between switches in a SONET ring network. As discussed above,current SONET networks require the same number of optical carrier leveltype of lines between nodes. The present invention, however, allows fordifferent combinations of optical carrier lines between switches,thereby providing greater network flexibility. Switch 410 has aplurality of ports and can split information from one line into manylines, or combine information from many lines and output the informationon a single line. As shown in FIG. 7, SONET ring network 700 hasswitches 710, 720, 730, and 740. The connections between these switchesare not the same for every span. For example, between switch 710 andswitch 720, there are two optical carrier 12 (OC-12) working lines ineach direction. Between switch 720 and switch 730, there is one OC-48working line going in each direction between the switches. Consistentwith the present invention, any combination of optical carrier levelsmay be combined between spans as long as the total capacity of the spanbetween two switches equals the total capacity between other switches inthe ring. In addition, the sum of the capacities of the working linesbetween two switches must equal the sum of the capacities of theprotection lines between the switches. In the ring network shown in FIG.7, for example, the sum of the optical capacities between each set ofswitches is a total of OC-48. This total may be reached using anycombination of OC carrier lines. For example, the spans between switches710 and 720 reach this total using four OC-12 lines while the spansbetween switches 720 and 730 reach this total using one OC-48 line.Switches 710, 720, 730, 740 direct traffic from a single OC-48 to fourOC-12 lines.

[0043] Moreover, in accordance with the present invention, lines mayeasily be added or removed from the ring. However, before a line is madeactive or inactive, the switches on both sides of the line determinewhether the line change maintains the required optical carrier capacitybetween switches. FIG. 8 shows the steps 800 performed by manager module413 when adding a line. First, a system administrator specifies the lineto make active by inputting a request, including a line identifier, intomanager module 413 at a switch at either end of the new line (step 810).This line ID must be the same on both ends of the line. All of theswitches identify the line using the same identifier, as discussed abovewith respect to FIG. 6. Manger module 413 determines the state of thespecified line from the monitor modules 424 (step 820). Monitor modules424 maintain information regarding the state of each line based on theline identifier. Lines are only used for actual transmission when in theactive state. The activating state refers to the state before monitormodules 424 on either side of a line have agreed to placing a line inthe active state. Similarly, the deactivating state is the state beforethe monitor module have agreed to placing a line in the inactive state.When a line is physically added, the monitor module 424 automaticallydesignates the line as being in an inactive state. If the line to beadded is in fact inactive, then the line is moved to the activated state(step 830). If however, the specified line is already in the activatingstate, then manager module 413 ignores the request (step 840). If theline specified is already active, then manager module 413 logs an errorin a central accessible log (step 850). If the specified line is in adeactivating state, then manager module 413 directs the monitor module424 to place the line back in the active state (step 860).

[0044]FIG. 9 shows the steps 900 performed by manager module 413 whendeleting a line. First, a system administrator specifies the line to bedeleted by inputting a request, including a line identifier, intomanager module 413 at a switch at either end of the line (step 910).Manager module 413 queries monitor module 424 to determine the status ofthe specified line (step 920). If the specified line is inactive, thenmanager module 413 takes an error in a central accessible log and doesnot take further action (step 930). If the designated line is in theactivating state, then manager module 413 directs monitor module 424 torevert the line to an inactive state (step 940). If the specified lineis in the active state, then manager module 413 directs monitor module424 to place the BLSR line in a deactivating state (step 950). If thespecified line is already in the deactivating state, then manager module413 ignores the request (step 960).

[0045]FIG. 10 shows steps 1000 performed by manager module 413 whenvalidating a new configuration of lines after lines have been added ordeleted. To validate the configuration, manager module 413 first sumsthe capacity of the lines associated with span west lines 416 that arein the active state or activating state (step 1020). The sum of thecapacity of the active lines in the span west lines 414 should equal thesummation of the capacity of the active lines in the span east lines416. Manager module 413 determines whether these sums are equal (step1030) and, if not, an error is generated and logged (step 1040). If thesums are equal, then manager module 413 directs monitor modules 424 tomove all of the lines in the activating state to the active state (step1050). Similarly, manager module 413 directs the monitor modules to moveall the lines in the deactivating state to the inactive state (1060).Manager module 413 in each switch in the ring network performs thischeck before validating any configuration.

[0046] Referring now to FIG. 4B in conjunction with FIG. 13, the CSDPcontroller 475 of the CSDP manager 415 can trigger the configurationmodule 455 to generate a CSDP Configuration (“Config”) message, which istransmitted around a ring (e.g., a VLSR or BLSR). Typically, thetransmission of the CSDP Config messages is initiated after a ringconfiguration change or initialization occurs. As each node receives theCSDP Config message, which was transmitted by the originating node, theother nodes can updates their topology table 470 with the topologyinformation contained within the received CSDP Config message.

[0047] In one embodiment, the CSDP Config message includes a message ID,a sequence number, a ring ID, a node ID, an east lines value, a westlines value, an east line info field and a west line info field. Themessage ID is used to identify the type of message and the version ofmessage (e.g., CSDP Config v. 1). The sequence number is used by thenodes to identify each CSDP Config message. The ring ID represents aunique identifier for the ring. The node ID represents a uniqueidentifier to the ring node. The east lines value represents the numberof working lines on the east span of the ring node. The west lines valuerepresents the number of working lines on the west span. The east lineinfo represents the line identifier and the number of line timeslots forthe east working line. The west line info represents the line identifierand the number of line timeslots for the west working line. By receivingthis information from each node on a ring, the CSDP modules 415 of aspecific node can generate a topology table 470 of the topology of thering.

[0048] To further illustrate the characteristics of the CSDP Configmessage, an embodiment of a virtual line switched ring (“VLSR”) 1300, asillustrated in FIG. 13, will be used for exemplary purposes. Typicallyin one embodiment of the present invention, upon the addition of a node,such as node 1310, into the VLSR ring 1300, the controller 412 willtrigger the CSDP controller 475 to initiate the configuration module 455to generate a CSDP Config message that includes configurationinformation about node 1310. As previously discussed, the CSDP Configmessage includes information such as the ring (e.g., VLSR1) to whichnode 1310 is being added, an identifier (e.g., SW1) representing alogical ring node representation for node 1310, the number of workinglines for the east span and west span lines of the node 1310 andinformation, including line identifiers and the number of line timeslotsfor the east span and west span lines.

[0049] Upon transmission of the CSDP config message onto the ring 1300(e.g., along the west span), the CSDP manager 415 takes advantage of thefact that as long as all of the intermediate nodes between the east andwest span of the originating node (e.g., nodes 1320, 1330 and 1340)forward a message correctly across the closed ring 1300, a message, suchas a CSDP Config message, which is sent in one direction (e.g., out thewest span of the node 1310), will ultimately be received in the otherdirection (e.g., at the east span of the node 1310). In one embodiment,CSDP messages, such as the CSDP config message, are transmitted over theworking line 1329W of the ring 1300 within the SONET protocol's DataCommunication Channel (“DCC”). To allow the CSDP manager 415 at eachnode within the ring 1300 to that the CSDP message is a CSDP configmessage, the message ID is set to CSDP Config v. 1. For the node 1310originating the CSDP message, the sequence number within the CSDP configmessage is used to match the message sent on the west span with themessage received back on the east span. For example, if the CSDP Configmessage with a specific sequence number, which was sent out of theoriginating node 1310, is not received back at the originating node onthe opposite span due to the break 1325 in the ring 1300, theoriginating node 1310 is able to determine that there is a problem withthe ring 1300. In addition, if multiple CSDP Config messages areoutstanding for the node 1310, only the message with the latest nodalinformation would be retransmitted.

[0050] When an addition, deletion or modification of a connection ortimeslot of a line associated with a node 1310 occurs, the CSDP manager415 of that node triggers the state module 460 to generate a new CSDPstate message with the new connection information (e.g., time slotinformation and port relationships) for the newly added, deleted ormodified connection. In one embodiment, each CSDP state messagetransmitted describes the connection information of a single connectionwithin the node 1310.

[0051] The information included within a CSDP state message includes amessage ID, a sequence number, a ring ID, a node ID, a span ID, a lineID, line timeslots information, timeslot concatenation state, timeslotadd/drop state, IS SDH, and ExcludeFixed. The message ID identifies thetype of message (e.g., CSDP State) and the version of message. Thesequence number is used to identify the specific CSDP state message,which was transmitted or received by a node. The ring ID is used toassign a unique identifier to the ring 1300. The node ID is used forassigning a unique identifier to the ring node. The span ID is used toidentify the span (e.g., east or west) to which this state pertains. Theline ID is used as a local line ID, which is assigned within the span,as to which the specific connection information pertains. The linetimeslots represent the number of STS-1 timeslots on this line (e.g., 1,3, 12, 48 or 192). The timeslot concatenation state informationrepresents the state of each STS-1 transmitted on this line including avalue representing the child of an associated STS-1 parent. With thistimeslot information, the CSDP state message can verify connectionsacross a span. The timeslot add/drop state can be used to represent thestate of each STS-1 transmitted on this line. In particular, thetimeslot add/drop state can be used to either delete a timeslot for suchpurposes as squelching a connection or for adding a connection entryinto the connections table 465.

[0052] The CSDP state message, like the CSDP config message, typicallyis transmitted in one direction around the ring 1300 on the workinglines (e.g., 1329W, 1326W, 1327W and 1328W) to the other CSDP modules415 at the intermediate nodes (e.g., 1320, 1330 and 1340). The CSDPstate message is used by these intermediate nodes to update each oftheir connections tables 465 with the new connection state informationof a specific line on a specific span of a ring node. This scheme allowsfor smaller message sizes and reduced message parsing complexity, whichthereby minimizes the network performance impact on the ring 1300. Uponreception of a CSDP state message, an intermediate node updates itslocal connections table 465 with the connection information specified inthe message. A node uses this connection state information for purposesincluding to detect addition and/or deletion of connections at eachnode, to store current concatenation information during a ring switchand to squelch connections during a “partial” ring switch situationresulting from node isolation or multiple span failures.

[0053] Should there be a need for a node to update either itsconnections table 465 or the topology table 470 (e.g., due to corruptionof the data in either table), the CSDP manager 415 of the node, whichneeds to updates its information, triggers the query module 450 togenerate CSDP query messages. CSDP query messages can be used by thatnode to request the latest configuration state or connection stateinformation from one or more other nodes. In particular, the CSDP querymessages include a message ID, a ring ID and a node ID. Upon receptionof the CSDP query message by the node designated by the node ID, thenode begins transmitting CSDP config messages and/or CSDP state messagesuntil it receives it's own messages back on its opposite span.

[0054] An embodiment of the present invention with regard to the CSDPManager 415 next will be described by way of example with reference toFIG. 13. Within ring 1300, working traffic originating at switch 1330and terminating at switch 1320 is passed along span 1325 in a east-westdirection as indicated by arrow 1326. If a break occurs in span 1326 (asindicated by an “X”), traffic is rerouted through switches 1310 and 1340using a protection line in span 1327, which is assigned in accordancewith processes and structures identified above. In this case, a K-bytering switch signal is supplied from switch 1330 to switch 1340 and thento switches 1310 and 1320 to thereby indicate use of the protection linein ring 1300, at least for particular time slots so affected by thebreak in span 1326. In particular, the traffic (e.g., timeslots) on thework line of the span 1326 is routed to the protect line on the othergood span 1327. The node 1340 at the other end of the good span enters aPass Through State where all the traffic entering on the protect line onspan 1327 is “Passed Through” to the protect line on the other spans1328, 1329.

[0055] On the Pass Through nodes 1340 and 1310, all timeslots on theeast span 416 of the protect line are connected to the timeslots on thewest span 414 of the protect line. However, there may be different sizedconnections (e.g., STS1, STS3c, STS12c etc.) on the work line, whichfailed due to the ring switch. This concatenation information,therefore, is passed to the Pass Through nodes 1340 and 1310 so thatthese nodes 1340 and 1310 can process the concatenation information. TheCSDP module 415 is responsible for communicating, via the configurationmodule 455, this concatenation information around the ring 1300. Alongwith timeslot information, the CSDP module 415 also utilizes theconfiguration module 455 to distribute additional topology informationaround the ring 1300 to each of the nodes. This enables the CSDP module415 for each node to auto discover the entire ring topology and to alertthe corresponding node if the ring 1300 is not configured properly. Whena node originates a CSDP config message or CSDP state message, the nodetransmits it on the east span. Intermediate nodes, after recording theconfiguration information for its own topology table 470, forward themessage around the rest of the ring until it terminates at theoriginating node. In one embodiment, if care is taken to avoidreordering messages, the sequence number can be ignored by intermediatenodes. In an embodiment, the CSDP messages normally are transmitted overa working line. During protection switches, the DCC can be automaticallyprotected via the protection line. In the event of a broken ring (nodefailure or multiple span failures not protected by partial ringswitches), however, CSDP information can not be reliably distributed, soCSDP messages are not sent. Once the ring reachieves connectivity, CSDPstate messages and CSDP config messages can be flooded to every node toupdate the connections table 465 and the topology table 470 with currentring and nodal information.

[0056] In conclusion, the SONET ring network of the present inventionuses switches as the network nodes to allow sharing a switch to connecta plurality of rings. A protection line between a plurality of rings isshared by utilizing overhead provided for in SONET standard protocols.Moreover, the shared protection line can be used by one ring over afirst time slot and a second ring over a second time slot. Thus,capacity which would otherwise be used for carrying dedicated protectiontraffic is utilized by additional working traffic instead. As a result,network capacity is increased without adding more physical lines.Furthermore, the present invention provides for having a differentnumber and type of lines between switches in a ring network by usingswitches and an algorithm to regulate the updating of the lines. Lastly,the present invention utilizes a CSDP messaging scheme to allow for eachnode on a ring to be able to generate and continually update itsconnections table and topology table to accurately reflect the currentcharacteristics of the ring(s) in which the node is connected.

[0057] Other embodiments, including utilizing the CSDP messages on amulti-ring network, will be apparent to those skilled in the art fromconsideration of the specification and practice of the inventiondisclosed herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

What is claimed is:
 1. A method for allowing a network element havingnetwork connections to a ring network to manage the network connections,the method comprising: sending a connection state message from thenetwork element around the ring network when the network element adds,deletes or modifies at least one timeslot within at least one of thenetwork connections; receiving the connection state message from thering network, the connection state message having been updated byintermediate network elements that are part of the first ring network;and managing the network connections connecting the network element tothe ring network by using the received connection state message.
 2. Themethod according to claim 1, said sending step sending the connectionstate message from the network element around the ring network when thenetwork element adds, deletes or modifies at least one of the networkconnections.
 3. The method according to claim 1, said managing includingdetecting the addition and/or deletion of timeslots at each of thenetwork elements connected to the ring network.
 4. The method accordingto claim 1, said managing including detecting the addition and/ordeletion of network connections at each of the network elementsconnected to the ring network.
 5. The method according to claim 1, saidmanaging including storing current concatenation information during aring switch operation of the ring network.
 6. The method according toclaim 1, said managing including squelching certain networkconnection(s) during a partial ring switch operation of the ringnetwork.
 7. The method according to claim 1, wherein the configurationmessage includes a message ID, a node ID, a span ID, a line ID, linetimeslots information, timeslot concatenation state, and timeslotadd/drop state information.
 8. The method according to claim 1, whereinthe network elements are capable of adding, dropping, passing through,and interchanging timeslots within the network connections.
 9. A methodof allowing the network element and the intermediate network elements tomanage their respective network connections to the ring networkaccording to claim 1, further comprising: at the intermediate networkelements, using the received connection state message to manage theirrespective network connections to the ring network.
 10. The methodaccording to claim 9, wherein the network connections including workingand protect network connections, wherein the network connections arepermitted to be of different bandwidths, wherein the configurationmessage includes timeslot concatenation information, the method furthercomprising: detecting failure of a span carrying one or more networkconnections; reconfiguring, based on the configuration message, networkelements adjacent to the failed span to reroute network traffic over theprotect network connections; and reconfiguring, based on theconfiguration message, the non-adjacent network elements not adjacent tothe failed span to pass through network traffic entering from theprotect network connections.
 11. A communications system for managingnetwork connections, comprising: a plurality of network elementsconnected in a ring network configuration via the network connections;at an originating network element, sending a connection state messagearound the ring network when the originating network element adds,deletes or modifies at least one timeslot within at least one of thenetwork connections; at the intermediate network elements, updating theconnection state message with topology information stored at each of theintermediate network elements; at the intermediate network elements,using the received connection state message to manage their respectivenetwork connections to the ring network; at the originating networkelement, receiving the connection state message from the ring network,the connection state message having been updated by intermediate networkelements that are part of the first ring network; and at the originatingnetwork element, managing the network connections connecting theoriginating network element to the ring network by using the receivedconnection state message.
 12. The system according to claim 11, whereinthe managing of the network connections performed by the networkelements includes detecting the addition and/or deletion of timeslots ateach of the network elements connected to the ring network.
 13. Thesystem according to claim 11, wherein the managing of the networkconnections performed by the network elements includes detecting theaddition and/or deletion of network connections at each of the networkelements connected to the ring network.
 14. The system according toclaim 11, wherein the managing of the network connections performed bythe network elements includes storing current concatenation informationduring a ring switch operation of the ring network.
 15. The systemaccording to claim 11, wherein the managing of the network connectionsperformed by the network elements includes squelching certain networkconnection(s) during a partial ring switch operation of the ringnetwork.
 16. The system according to claim 11, the configuration messageincludes a message ID, a node ID, a span ID, a line ID, line timeslotsinformation, timeslot concatenation state, and timeslot add/drop stateinformation.
 17. The system according to claim 11, said network elementsbeing capable of adding, dropping, passing through, and interchangingtimeslots within the network connections.
 18. The system according toclaim 11, wherein the network connections including working and protectnetwork connections, wherein the network connections are permitted to beof different bandwidths, wherein the configuration message includestimeslot concatenation information, at least some of said networkelements detecting failure of a span carrying one or more networkconnections; said network elements that are adjacent to the failed spanreconfiguring, based on the configuration message, to reroute networktraffic over the protect network connections; and said networkelement(s) that are not adjacent to the failed span reconfiguring, basedon the configuration message, to pass through network traffic enteringfrom the protect network connections.